1. Field of the Invention
The present invention relates to a X-ray fluorescence analysis and an X-ray fluorescence spectrometer for analyzing fluorescent X-rays emitted from a substance of interest present on a surface of a sample to be analyzed such as, for example, a silicon substrate.
2. Description of the Prior Art
For the determination of the identity and/or the abundance of at least one contaminant that is a substance of interest deposited on a surface of, for example, a silicon substrate, the total reflection X-ray fluorescence analysis has long been employed. In order to analyze a contaminant of a transition metal, particularly iron, nickel, copper or zinc of a kind found in the vicinity of the surface of the silicon substrate as a substance of interest, the use has been made of, for example, W-Lxcex2 lines as primary X-rays. Such lines are projected so as to be incident upon the surface of the silicon substrate at a minute angle of incidence so that the identity of such transition metal can be determined in terms of the quantity of energies of the fluorescent X-rays emitted from the substance of interest and the abundance of such transit metal can be determined in terms of the strength of the fluorescent X-rays emitted from the substance of interest.
However, the substance of interest, of which the identity and/or the abundance are to be determined, is deposited in various ways or distribution manners on the surface of the silicon substrate having an oxide film formed thereon. For example, the substance of interest may be distributed in the form of a film on the oxide film of SiO2 as shown in FIG. 4A, in the form of grains on the oxide film of SiO2 as shown in FIG. 4B, or in the form as distributed randomly within the oxide film of SiO2 and/or at the interface between the oxide film of SiO2 and the substrate of Si as shown in FIG. 4C. Accordingly, even though the abundance of the substance of interest remains the same, measurement of the strength of the fluorescent X-rays emitted as a result of excitation by the predetermined primary X-ray varies depending on the manner of distribution of the substance of interest. For this reason, the abundance of the substance of interest calculated on the basis of the measured strength of the fluorescent X-rays varies as well depending on the manner of distribution of the substance of interest and, therefore, the total reflection X-ray fluorescence analysis is incapable of giving an accurate abundance of the substance of interest.
Accordingly, the present invention has been devised with a view to substantially eliminating the above discussed problems and is intended to provide a fluorescent X-ray analyzing method and a X-ray fluorescence spectrometer capable of accurately measuring the abundance of the substance of interest present in a sample to be analyzed.
In order to accomplish the foregoing object of the present invention, there is provided a fluorescent X-ray analyzing method for measuring fluorescent X-rays emitted from a substance of interest present on a surface area of a sample by irradiating the surface area of the sample with primary X-rays. This X-ray analyzing method includes measurement of a strength of fluorescent X-rays by projecting the primary X-rays onto standard samples 1 and 2 having different distribution of the substance of interest, but having the same abundance of the substance of interest, so as to impinge thereupon at a plurality of different glancing angles of xc3x81 to xc3x8n.
Then, using two glancing angles xc3x8a and xc3x8b (where xc3x8a less than xc3x8b) arbitrarily chosen from the plural glancing angles, a ratio between the strengths Ia1 and Ib1 of the fluorescent X-rays, emitted from the standard sample 1 when irradiated at respective angles xc3x8a and xc3x8b, is determined as a grading coefficient PF1 of the standard sample 1 and a ratio between the strengths Ia2 and Ib2 of the fluorescent X-rays, emitted from the standard sample 2 when irradiated at angles xc3x8a and xc3x8b, is determined as a grading coefficient PF2 of the standard sample 2. In the present invention, the ratio of the strengths of the fluorescent X-rays emitted from a single substance of interest determined at those two glancing angles is defined as a grading coefficient PF. The grading coefficient PF so defined represents distribution of the substance of interest.
Thereafter, in order to render the value of Ia2xc2x7PF1/PF2 to approach the value of Ia1, or to render the ratio Ia1/Ia2 to approach the ratio PF1/PF2 between the determined grading coefficients of the standard samples 1 and 2, the specific glancing angles xc3x8a* and xc3x8b* are determined and the abundance of the substance of interest is determined from the respective strengths Ia3 and Ib3 of the fluorescent X-rays of a sample to be measured that is irradiated at the determined specific glancing angles xc3x8a* and xc3x8b*.
The X-ray fluorescence spectrometer of the present invention disclosed herein is for measuring fluorescent X-rays emitted from a substance of interest present on a surface area of a sample by irradiating the surface area of the sample with primary X-rays. This fluorescence spectrometer includes a measuring unit for measuring a strength of fluorescent X-rays by projecting the primary X-rays onto standard samples 1 and 2 having different distribution of the substance of interest, but having the same abundance of the substance of interest, so as to impinge thereupon at a plurality of different glancing angles of xc3x81 to xc3x8n. The fluorescence spectrometer further includes a calculating means for determining a ratio between the strengths Ia1 and Ib1 of the fluorescent X-rays, emitted from the standard sample 1, for two glancing angles xc3x8a and xc3x8b (where xc3x8a less than xc3x8b) arbitrarily chosen from the plural glancing angles, as a grading coefficient PF1 of the standard sample 1, and also determining a ratio between the strength Ia2 and Ib2 of the fluorescent X-rays, emitted from the standard sample 2, for those two glancing angles xc3x8a andxc3x8b, as a grading coefficient PF2 of the standard sample 2, and then determining the corresponding specific glancing angles xc3x8a* and xc3x8b* (xc3x8a* less than xc3x8b*) at which the ratio of Ia2xc2x7PF1/PF2 can take a value approximating to Ia1; and an abundance determining unit for determining the abundance of the substance of interest from strengths Ia3 and Ib3 of the fluorescent X-rays emitted from a sample to be measured when the latter is irradiated with the primary X-rays at respective glancing angles xc3x8a* and xc3x8b* so determined.
According to the present invention, since the specific glancing angles xc3x8a* and xc3x8b* are so determined that the value of the fluorescent X-ray strength Ia2 of the standard sample 2 multiplied by the ratio PF1/PF2 between the respective grading coefficients of the standard samples 1 and 2 can approach the value of the fluorescent X-ray strength Ia1 of the standard sample 1 and the abundance of the substance of interest is then determined based on the fluorescent X-ray strengths Ia3 and Ib3 given by the sample to be measured that is irradiated at the determined specific glancing angles xc3x8a* and xc3x8b*, the abundance of the substance of interest can be accurately determined regardless of the distribution thereof. The specific glancing angles xc3x8a* and xc3x8b* are chosen to be so minute as to suite for total reflection at the surface of area of the sample to be measured.
In the practice of the present invention, a status in that the value of Ia2xc2x7PF1/PF2 approaches the value of Ia1 means that the coefficient A represented by (Ia2/Ia1)xc2x7(PF1/PF2) approaches 1. As the coefficient A approaches 1, it is possible to highly accurately determine the abundance of the substance of interest. The coefficient A may be within the range of 0.3 to 3, preferably within the range of 0.4 to 2.5, particularly preferably within the range of 0.7 to 1.5, and more preferably within the range of 0.8 to 1.2.
Preferably, the manner in which the substance of interest is distributed is determined based on the ratio or difference between strengths of the fluorescent X-rays emitted from the sample that is irradiated with the primary X-rays at at least two glancing angles.